Credit system in OpenPiton

[Anirudh Krishna]

Hello everyone!

I am working on a project in which I have successfully inserted a module between the L1.5 cache and the NOC router.

I was able to send a message from the core, to this module, and I can see that the module is receiving this message. However, I notice that after the message is received, no further messages are being sent from the core. 
I would like to understand the credit system better, as it seems like I am not adding credits back once my message has reached the module. That is, it seems like credits once consumed are not replenished. 
Please help me understand the credit system!

[Jonathan Balkind]

Hi Anirudh,

There are quite a few details you need to be careful with here. Any modification to the network must ensure that it maintains the original point-to-point ordering requirements. It's also the case that when the core starts up, it is probably only making a single request at a time to the memory system because the bootrom is considered "non-idempotent" in RISC-V terms. If you drop the request or delay it indefinitely, the core may just be sitting there waiting for the response.

I'm also not sure whether you're talking about the L1.5's credits or the NoC's credits?

Thanks,

Jon

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[Anirudh Krishna]

Hi Jon,

I was referring to the NOC1's credits (the creditman_noc1_avail, I believe it is the NOC1s credit system but I may be mistaken). 

And yes, I think it is the case that the core is just waiting for the response.

However, I noticed that there are still credits available after my message has been sent, so my intuition is that the cause may be something else.

It would be great if you could point me to some resource where I can learn more about the specific credit implementation used in the network!